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Trusted Contributor
IOS2JunOS
Posts: 92
Registered: ‎10-17-2008
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Same BGP ASN in two locations

[ Edited ]

We have a setup where we have the same ASN in two different locations. I have configured “autonomous-system 1234 loops 2” under routing-options in both locations and I’m seeing some weird behavior.
Each side is advertising their own /24 to the provider.
it’s the same provider in both location with sideA having one additional provider. I see SideA receiving SideBs /24 but not vice versa and if I clear BGP session with the provider the situation reverses where SiteB now is receiving SiteAs /24 prefix but not the other way around. It’s very strange.  Is there any other way to set this up? TIA

Recognized Expert
mhariry
Posts: 340
Registered: ‎06-01-2011
0

Re: Same BGP ASN in two locations

Hi Dear,

 

You have mentioned that Side A is connected to two ISPs. You have to specify which on is the primary and which one is the backup cause if the second ISP (the not common one) is the primary so you need to increase the number os loops 

 

you could increase the number anyway and check the result just for testing

 

Thanks,

Mohamed Elhariry

JNCIE # 1059, CCNP, CCIP

Regards,
Mohamed Elhariry
2* JNCIE (SEC # 159, SP # 1059),JNCIP-ENT

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Contributor
karlr
Posts: 37
Registered: ‎09-20-2010
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Re: Same BGP ASN in two locations

I would set up IBGP between the 2 locations. Im not familiar with the loops statement, but it seems to be a workaround for the fact that BGP in normal setup will not accept any outes with its own ASN in the as-path?

 

regards

Karl

 

 

Recognized Expert
mhariry
Posts: 340
Registered: ‎06-01-2011
0

Re: Same BGP ASN in two locations

As you are using in both branches same AS path so by default it will consider BGP loop according to BGP attribute and the route will be rejected not even installed in the routing table as a hidden route

 

to solve this problem we have to solution

 

1- ask the ISP to solve this problem by using (set protocols BGP group x as-override) it will override your AS by the ISP AS so no loops appears anymore

 

2- configure (set routing-options autonomous-system loops n) and you mentioned u r already using this command but you permit this allowance till just 2 AS-path after that it will consider loop. That's why from your problem description I asked you to mentioned in the branch which have dual connection to two ISPs you are using the same ISP on the other branch as a main link or backup. Because if you are using different link the as-path will be more than two as-path. Could you please increase the no. to 6 for example and check the result (set routing-options autonomous-system loops 6).

 

Thanks,

Mohamed Elhariry

JNCIE-M/T # 1059, CCNP, CCIP

Regards,
Mohamed Elhariry
2* JNCIE (SEC # 159, SP # 1059),JNCIP-ENT

[Click the "Star" for Kudos if you think I earned it!
If this solution worked for you please flag my post as an "Accepted Solution" so others can benefit..]
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